Johnson said the corporation treated eurosceptic views as "if they were vaguely mad and unpleasant" and "completely ignored" the private sector.

Outgoing BBC director general Mark Thompson has said the corporation was guilty of a "massive bias to the left" in the past. He told the New Statesman that staff were "quite mystified" by the rise of Margaret Thatcher but now there was "less overt tribalism" among its journalists.

"Our approach means asking difficult questions of politicians, businesses and unions alike. People with trenchant views often find this process uncomfortable but our audience expects us to challenge those in power as well as those who seek it" the spokesman added.

Ian Austin MP says he hasn't noticed any pro-Labour bias in the BBC.

Some have reacted with scepticism to Johnson's claim of BBC bias. Paul Lewis pointed out that the Mayor himself is 'funded by taxpayers'.

Others have responded by pointing out the fact that the Chairman of the BBC Trust, Chris Patten, used to be a Tory minister.